Low liquid level detecting device and method

ABSTRACT

The invention discloses a low liquid level detecting device comprising a float sensor and a casing. The casing has first to third chambers formed between an upper wall and a bottom wall. The top portion of the first chamber is formed with a top opening. The bottom portion of the first chamber communicates with the bottom portion of the second chamber. The top portion of the second chamber communicates with the top portion of the third chamber. The bottom portion of the third chamber is formed with a bottom opening. A float sensor is mounted inside the third chamber. A drain hole is formed through the bottom part of a chamber wall surrounding the third chamber. A method for detecting a low liquid level using the above low liquid level detecting device is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. application Ser. No.11/986,497, now U.S. Pat. No. 7,748,269, that was filed on Nov. 20,2007, is entitled “LOW LIQUID LEVEL DETECTING DEVICE AND METHOD”, andclaims foreign priority under Title 35, United States Code, §119(a)-(d)or §365(b) to Chinese Patent Application No. 200710072850.2, which wasfiled on Jan. 11, 2007 into the State Intellectual Property Office ofthe People's Republic of China.

TECHNICAL FIELD

The present invention relates to the field of liquid level detecting,especially to a detecting device and a detecting method for detectingthe level of a liquid, such as a consumable liquid material, whichshould not be or cannot be transferred between different containers.

BACKGROUND

In medical and surgical detection equipments, when there is a consumableliquid material that should not be or cannot be transferred betweendifferent containers, a liquid level detecting device is usuallyprovided for detecting a certain low level of the liquid. An objectivein the design of a detecting device is that the detecting deviceresponds to a small volume or level of remaining or residual liquid,thus the consumption rate of the consumable material can be increased.

In known low liquid level detecting devices, float sensors are generallyused for detecting liquid levels. In a float sensor, a float body movesup and down with the liquid surface, thus a magnetic ring enclosed inthe float body also moves up and down. When the liquid level in thecontainer is high, the float body is at a high position. On the otherhand, when the liquid level in the container falls down to a certainextent, the magnetic ring, falling together with the float body,initiates a magnetic switch by magnetic induction. The magnetic switchsends a signal to a control circuit, which detects out that the liquidlevel in the container reaches to a low condition.

In such a float sensor, under the limitation of the above magneticinduction principle, the float sensor is generally bulky. Meanwhile,since the weight of the float body is high, the lowest liquid levelnecessary to cause the lowering float body initiating the magneticswitch is relatively high. In this condition, during detection, when thesensor responds to the float body moving close to the bottom portion ofthe container, the level of the remaining liquid in the container isstill relatively high, which results in that it cannot effectivelyreflect whether the liquid level really reaches to the bottom portion ofthe container.

SUMMARY OF INVENTION

An object of the present invention is to overcome the above shortagesexisted in the prior art by providing a low liquid level detectingdevice and a corresponding method which are effective at a very lowlevel of the remaining or residual liquid in the container, and thus theconsumption rate of the liquid can be increased.

To achieve the above object, the present invention, in one aspect,provides a low liquid level detecting device comprising a float sensorand a casing, wherein the casing has a top wall, a bottom wall and afirst chamber, a second chamber and a third chamber formed between theupper and bottom walls and separated from each other, the top portion ofthe first chamber is formed with a top opening, the bottom portion ofthe first chamber communicates with the bottom portion of the secondchamber via a first connection passage, the top portion of the secondchamber communicates with the top portion of the third chamber via asecond connection passage, the bottom portion of the third chamber isformed with a bottom opening, afloat sensor is mounted inside the thirdchamber, and a drain hole is formed through the bottom part of a chamberwall surrounding the third chamber.

According to an embodiment of the present invention, preferably, thedrain hole is formed down to the bottom surface of the casing, and theheight of the drain hole is set to be smaller than the distance betweenthe highest point of the first connection passage and the bottom surfaceof the casing.

According to an embodiment of the present invention, preferably, theheight of the drain hole is not larger than the distance between thelowest point of the first connection passage and the bottom surface ofthe casing.

According to an embodiment of the present invention, preferably, thehighest point of the second connection passage is lower than the topsurface of the casing.

According to an embodiment of the present invention, preferably, thefirst chamber, the first connection passage and the second chamber forma substantial “U” shape, and the second chamber, the second connectionpassage and the third chamber form a substantial inverted “U” shape.

According to an embodiment of the present invention, preferably, whereinthe float sensor comprises a guiding bar, a magnetic switch and a floatbody with a magnetic ring fixed to it, the guiding bar is fixed insidethe third chamber and extends in a vertical orientation, the magneticswitch is fastened to a lower part of the guiding bar, and the floatbody loosely surrounds the guiding bar and is able to move up and downalong the guiding bar under the action of the buoyance of the liquid inthe third chamber.

The present invention, in another aspect, provides a method fordetecting a low liquid level using the low liquid level detecting deviceof the invention, wherein the low liquid level detecting device isimmersed in a liquid to be detected, such that the first chamber, thesecond chamber, and the third chamber is filled with the liquid; then,as the level of the liquid to be detected falls down and below the topopening of the first chamber, the liquid in the first chamber, thesecond chamber and the third chamber flows out from the device throughthe drain hole, thus the liquid surface in the first chamber falls downtogether with the level of the liquid to be detected, but the liquidsurfaces in the second chamber and the third chamber remain unchanged;and when the level of the liquid to be detected falls down to a heightlower than the highest point of the first connection passage, the liquidin the second chamber and the third chamber flows quickly out from thedevice through the drain hole, thus the float sensor detects out the lowliquid level.

According to an embodiment of the present invention, preferably, thefloat sensor comprises a guiding bar, a magnetic switch and a float bodywith a magnetic ring fixed to it, the guiding bar is fixed inside thethird chamber and extends in a vertical orientation, the magnetic switchis fastened to a lower part of the guiding bar, and the float bodyloosely surrounds the guiding bar and is able to move up and down alongthe guiding bar under the action of the buoyance of the liquid in thethird chamber, and wherein the float body remains at the top position ofits vertical stroke until the level of the liquid to be detected fallsbelow the highest point of the first connection passage.

According to an embodiment of the present invention, preferably, afterthe level of the liquid to be detected falls down to a height lower thanthe highest point of the first connection passage, as the liquid in thesecond chamber and the third chamber flows quickly out through the drainhole, the float body falls down rapidly and impacts onto the magneticswitch and thus initiates the magnetic switch, so that the magneticswitch sends out a signal to a control circuit which detects out thatthe level of the liquid to be detected reaches to low liquid level.

According to an embodiment of the present invention, preferably, whenthe low liquid level detecting device is immersed in the liquid to bedetected, all or most of the air in the first to the third chambers isexpelled out.

The present invention can thus obtain advantages over the prior art.Specifically, the casing and the float sensor are integrated in thedevice and form a vessel in fluid communication with the liquidcontainer, so that the float body of the float sensor responds to a verylow liquid level in the container. Thus the problem existed in the priorart, i.e., the float sensor only detects when a large quantity of liquidis still remained in the container due to the size and inductionprinciple of it, can be overcome by the present invention. Meanwhile, bycontrolling the level of the remaining liquid to be detected by settingthe distance from the highest point of the first connection passage tothe bottom portion of the container, a significantly lowered level ofthe remaining liquid to be detected is allowed, thus the consumptionrate of the consumable liquid material can be increased.

BRIEF INTRODUCTION TO THE DRAWINGS

The present invention will be described in details with reference to thedrawings in which:

FIG. 1 is a principle diagram of an embodiment of the present invention;and

FIG. 2 is a schematic sectional view of the structure of the low liquidlevel detecting device of the embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The operation principle of the low liquid level detecting device of anembodiment of the present invention and the corresponding detectingmethod is schematically shown in FIG. 1. Specifically, a curved pipe 1is arranged in the container 2. The container 2 is previously or is thenfilled with a liquid 3. The curved pipe 1 comprises a first straightpipe section 11, an arcuate first connection pipe section 12, a secondstraight pipe section 13, an arcuate second connection pipe section 14and a third straight pipe section 15. The upper end of the firststraight pipe section 11 has a top opening 16 for communicating with theoutside atmosphere, and the lower end of the first straight pipe section11 is connected with the lower end of the second straight pipe section13 via the first connection pipe section 12.

The upper end of the second straight pipe section 13 is connected withthe upper end of the third straight pipe section 15 via the secondconnection pipe section 14. The lower end of the third straight pipesection 15 has a bottom opening 17 for communicating with the innervolume of the container 2. The first straight pipe section 11, the firstconnection pipe section 12 and the second straight pipe section 13 forma substantial upright “u” shape, the second straight pipe section 13,the second connection pipe section 14 and the third straight pipesection 15 form a substantial inverted “u” shape.

When the curved pipe 1 is arranged in the container and is immersed inthe liquid 3, since the top opening 16 at the upper end of the curvedpipe (i.e. the opening of the first straight pipe section 11)communicates with the outside atmosphere and the bottom opening 17 atthe lower end communicates with the inner volume of the container (i.e.,the lower end communicates with the inner volume of the container viathe bottom opening of the third straight pipe section), the curved pipe1 forms a fluid communication vessel with the container 2, whereby thecurved pipe is filled with liquid. After the liquid level in thecontainer is reduced to be lower than the top opening 16, the liquidsurface in the first straight pipe section 11 will be lowered togetherwith the liquid level in the container under the influence of theatmosphere pressure, while the liquid surfaces in the second straightpipe section 13 and the third straight pipe section 15 remain unchangedwithout being lowered.

Then, when the liquid level in the container is of the same height as ora little lower than the highest point P of the first connection pipesection 12 (i.e. the point in the first connection pipe section whichhas a maximum vertical distance from the bottom portion of thecontainer), the liquid in the second straight pipe section 13 and thethird straight pipe section 15, under the influence of the atmospherepressure, will lose its equilibrium suddenly, and the liquid in thecurved pipe 1 will suddenly flow in a direction shown by the arrows inFIG. 1 and drain out from the bottom opening 17 of the third straightpipe section. Thus, it can identify that the height of the liquid level(surface) of the container is now corresponding to the height H of thehighest point P from the bottom portion of the container. In practice,the height H can be set to be very small.

Referring to FIG. 2, a low liquid level detecting device according to anembodiment of the present invention comprises a casing 4 and a floatsensor 5. The casing 4 has a horizontal top wall 46, a horizontal bottomwall 47, and a first chamber 41, a first connection passage 42, a secondchamber 43, a second connection passage 44 and a third chamber 45 formedbetween the upper and bottom walls 46, 47. A top opening 411communicating with the outside atmosphere is formed at the top portionof the first chamber 41 (the top opening 411 is opened in the topsurface of the casing top wall 46).

The bottom portion of the first chamber 41 communicates with the bottomportion of the second chamber 43 via the horizontal first connectionpassage 42. The top portion of the second chamber 43 communicates withthe top portion of the third chamber 45 via the horizontal secondconnection passage 44. A bottom opening 451 is formed in the bottomportion of the third chamber 45 (the bottom opening 451 is opened in thebottom surface of the bottom wall 47 of the casing). The first chamber41 and the second chamber 43 are separated from each other by a verticalfirst partition wall 48, and the second chamber 43 and the third chamber45 are separated from each other by a vertical second partition wall 49.In a vertical section, the first chamber 41, the first connectionpassage 42 and the second chamber 43 form a substantial “U” shape, whilethe second chamber 43, the second connection passage 44 and the thirdchamber 45 form a substantial inverted “U” shape.

Further, in the condition that the casing 4 is put on the bottom portionof a container so that bottom wall 47 of the casing is attached to thebottom portion of the container, a drain hole 40 formed through thebottom part of a vertical chamber wall surrounding the chamber 45 allowsthe liquid flow into or out from the third chamber. The drain hole 40 iscut down through the bottom wall 47 of the casing. The float sensor 5comprises a guiding bar 51, a magnetic switch 52, and a float body 53with a magnetic ring fixed to it. The guiding bar 51 is fixed in avertical orientation in the third chamber 45, and the magnetic switch 52is fastened to a lower part of the guiding bar 51.

The float body 53 loosely surrounds the guiding bar 51 so as to move upand down along the guiding bar 51 under the action of the buoyance ofthe liquid in the third chamber. The first connection passage, which isa slot through the first partition wall, also creates a clearancebetween the first partition wall and the bottom portion of the casing,which clearance corresponding to the first connection passage. Thesecond connection passage, which is a slot through the second partitionwall, also creates a clearance between the second partition wall and thetop portion of the casing, which clearance corresponding to the firstconnection passage. In this embodiment, the third chamber has both thebottom opening formed in the bottom surface of the bottom wall of thecasing and the drain hole extending horizontally through the verticalchamber wall of the chamber. However, it can be understood that thethird chamber may only have one of the opening and the drain hole. Whenonly the drain hole is provided, the drain hole functions as the bottomopening for discharging the liquid from the third chamber.

Now a method for detecting a low liquid level using the above describedlow liquid level detecting device, or the operation procedure of the lowliquid level detecting device, will be described. First, the wholedevice is put onto the bottom portion of a container (i.e., the bottomsurface of the casing is attached to the bottom portion of thecontainer). The container is previously or is then filled with a liquidsuch that-the whole device is immersed in the liquid. Since the casing 4forms a fluid communication vessel with the container, all the chambers41, 43 and 45 and both the connection passages 42, 44 are filled withliquid. Now, under the action of the buoyance of the liquid, the floatbody 53 of the float sensor is at the top position of its verticalstroke along the guiding bar 51.

With the liquid level in the container gradually falling down, theliquid level in the container becomes lower than the top opening 411 ofthe device, then the liquid surface in the first chamber 41 falls downtogether with the liquid level in the container, but the liquid surfacesin the second chamber 43 and the third chamber 45 do not fall down. Thefloat body 53 remains at the top position of the vertical stroke, untilthe liquid surface in the first chamber 41 (corresponding to the liquidlevel in the container) reaches down to the highest point Ph of thefirst connection passage 42 (i.e., the point having the largest verticaldistance from the bottom portion of the container, which also having thelargest vertical distance from bottom wall 47 of the casing).

At this point, or with the liquid level in the container falls furtherdown a little, the liquid in the second chamber 43 and the third chamber45 quickly flows out through the drain hole 40 at the bottom portion ofthe third chamber and the second and third chambers are evacuated, itfollows that the float body 53 of the float sensor falls rapidly underthe action of gravity along the guiding bar 51 to bottom position of thevertical stroke so as to impact the magnetic switch 52 and initiates themagnetic switch 52. The magnetic switch 52 sends out a signal to acontrol circuit, which judges out that the liquid level in the containerreaches to a low liquid level or becomes proximate to the bottom portionof the container.

The height of the level of the remaining liquid in the container canthus be controlled by the device by setting the vertical distance H1between the highest point Ph of the first connection passage 42 and thebottom portion of the container (i.e., the vertical distance H1 betweenthe highest point Ph and the bottom surface of the bottom wall 47 of thecasing). In practice, this distance H1 can be set to be very small, thusthe quantity of the remaining liquid in the container can be very small.In the device, the height h of the drain hole 40 should be smaller thanthe distance H1, and preferably the height h of the drain hole 40 is notlarger than the vertical distance H2 between the lowest point P1 and thebottom surface of the container, or h≦H2, thus the liquid in bothconnection passages 42, 44 can be drained out in a largest extent.

Furthermore, the highest point of the second connection passage 44 islower than the top opening 411 of the first chamber 41 (i.e., thehighest point of the second connection passage is lower than the topsurface of the top wall 46 of the casing), so as to expel all or most ofthe air from the three chambers 41, 43 and 45 when the device isimmersed in the liquid in the container. At this end, it should be notedthat, after the device is immersed in the liquid in the container, evenif a small amount of air is existed in the upper portions of the thirdchamber 45 and the second connection passage 44, the device alsofunctions stably.

The present invention is described with reference to its preferredembodiments which are not intended to restrict the scope of the presentinvention. A skilled in the art will readily recognize thatmodifications and changes can be made to the embodiments withoutdeparting from the spirit of the present invention, and accordingly allthese modifications and changes may be regarded as falling within thescope of the present invention.

We claim:
 1. An apparatus for detecting fluid level, comprising: a fluidcontainer; a float sensor that is disposed inside the fluid container tomeasure a fluid level in the fluid container, wherein the fluid levelvaries when an amount of fluid in the fluid container varies; a lowfluid level detection device that is at least partially disposed in thefluid container and comprises a fluid passageway, wherein one end of thefluid passageway is open to atmosphere at at least one point duringdetection of the fluid level, the fluid passageway comprises a pluralityof fluid passageway segments, in which each segment of the fluidpassageway segments communicates with at least another segment of thefluid passageway segments, and a height of the fluid in at least one ofthe plurality of fluid passageway segments remains unchanged when thefluid level in the container varies but remains at or above apredetermined level.
 2. The apparatus for detecting fluid level of claim1, wherein one end of the fluid passageway is located above the fluidlevel.
 3. The apparatus for detecting fluid level of claim 1, whereinanother end of the fluid passageway is disposed close to a bottomsurface of the container.
 4. The apparatus for detecting fluid level ofclaim 1, wherein at least two of the plurality of fluid passagewaysegments are to be filled with a fluid in the fluid container duringdetection of the fluid level of the fluid.
 5. The apparatus fordetecting fluid level of claim 1, wherein the low fluid level detectiondevice is to indicate a low fluid level based at least in part upon acriterion.
 6. The apparatus for detecting fluid level of claim 5,wherein the criterion comprises an indication of change in the height ofthe fluid in the at least one of the plurality of fluid passagewaysegments.
 7. The apparatus for detecting fluid level of claim 6, whereinthe height of the fluid in the at least one of the plurality ofpassageway segments begins to change when the fluid in the containerreaches or drops below a predetermined level.
 8. The apparatus fordetecting fluid level of claim 1, further comprising: a dischargingdevice that is to drain, discharge, or empty the fluid from the fluidcontainer.
 9. The apparatus for detecting fluid level of claim 1,wherein another end of the fluid passageway is submerged in the fluidduring at least a period of time for detection of the fluid level. 10.The apparatus for detecting fluid level of claim 1, wherein the floatsensor comprises: a guiding bar, a magnetic sensor, and a float body,wherein the guiding bar is to allow the float sensor to move along withchanges in the liquid level, and the magnetic sensor is attached to theguiding bar and senses a position of the float body.